It has become commonplace to package and sterilize medical and surgical implements in individual packages, whereby the implements are maintained in a sterile condition until used. A pre-sterile item may be placed into a sterile package to provide a sterile environment, but the most common practice is to sterilize the item within a package or a container. The latter procedure typically involves exposure of the package to an active sterilant such as steam or ethylene oxide.
Since an active sterilant must penetrate into the interior of a package to be effective on the interior of the package and articles therein, it is desirable that the package be sufficiently porous to enable penetration of the sterilant into the package as well as purging of residual gas from the package. At the same time, the porosity must be sufficiently low to prevent penetration of bacteria into the package after sterilization.
Various packages have been proposed to accomplish the above objectives, including packages or pouches composed partially of thermoplastic films and partially of a more porous material, such as paper or a porous polyolefin material. Pouches of this nature are described in the following patents: U.S. Pat. Nos. 3,247,957; 3,338,019; 3,472,369; 3,547,257; 3,627,611 and 3,685,720. In all of the above patents, a window, seam or empty panel of a thermoplastic film pouch is covered by a porous sheet material to facilitate venting of the pouch during the sterilization procedure.
In the formation of pouches from thermoplastic films, it is customary to heat seal plies of film together along lines of seal to provide a composite package. A problem which frequently arises, however, is the inability to obtain a seal of uniform integrity when a plurality of plies of film and porous materials are sealed together simultaneously. This problem becomes acute when one or more of the inner plies terminates within the seal area. The void created at the end of the discontinuous ply must be closed or one or more passageways from the exterior into the interior of the package can be established, thereby destroying the integrity of a sterile condition within the package. This problem frequently arises when a porous sheet is incorporated at one end of the package or pouch.